Circular mean smoothing using BandMath

I would like to apply a circular kernel / mean smoothing to an image, and I found out that the kernel in the Smoothing app is square.

How can I do this using BandMath ? I read that I can declare a kernel in a separate txt file, but what would be the expression to apply this as a focal mean to each pixel ?

So I tried to do this alone, declaring a kernel in txt file and using dotpr.
The problem : I need a 12 pixel radius, and I just found out the im1b1Nkxp syntax does not accept 2 digits neighbor sizeā€¦!
Is there another way ?